I don't know but I've been using this technique for a year or two now with great success. The Google authenticator just stores its secrets in the salute db every app gets.
Autocorrect kicked in there... sqlite* (it is absurdly difficult to put an asterisk at the end of a message on HN. it seems to require a trailing whitespace[1] for it to show up, however the input is trimmed, so...)
I have not, but I have extracted the backup with https://sourceforge.net/projects/adbextractor/ and inspected the contents, visually confirming the secrets are there. Even if a restore doesn't work, I can re-enter them manually from the information in the sqlite database. However I fully expect a restore to work.
Thats exactly why I copy and save every 2fa QR Code in my KeePass database, along with backup codes. Phone changed? No worries, install Google Auth, rescan those QRs, and voila, your 2fa system is back and running !! :)
Most 2FA services that allow authenticators offer recovery codes. I keep the recovery code saved in my password manager, and if I ever lost my phone I use that to log into the site and then get a new QR code.
Yes, that's also a way, but why not save the QR code first time you see it, instead of loosing it, resetting with recovery code, and then again getting a new one? Recovery codes are fine, and should be kept safe and such, but also the Original QR code can also be saved and screenshot. That way, phone lost? open database, load QR code, scan in new phone.
I have used Yubico's U2F key since shortly after they came out (Nov 2014). They are very robust and relatively cheap. Moreover, in contrast to some cheaper keys, they require physical confirmation by a finger press.
